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Proper Engine Running Temperature
#1374806 Tue Aug 25 2020 06:11 PM
Joined: Apr 2019
Posts: 11
R
New Guy
Good Morning;
I have a 1941 GMC 3/4 ton Pick up with a 248 cu inch engine. It now has an aluminum radiator, Air Conditioning; but retains the original 4 speed transmission. The Gauge Cluster with the capillary temperature gauge shows the top temperature of 212 degrees F. The engine which was rebuilt and now has approximately 1000 miles runs around the 200 degree F range.

What is the proper temp range of the thermostat that I should be running?
What is the proper pressure range of the radiator cap that I should be using
Do I have a problem with the engine running in the 190-205 degree F range?

Seems as if the temp comes up to very close to 210 degrees F; then backs down to 180-190 as long as I keep moving (electric fan installed; stock fan removed)



thanks for the help.

Re: Proper Engine Running Temperature
RogerB1941GMC #1374814 Tue Aug 25 2020 07:51 PM
Joined: Nov 2005
Posts: 5,775
3
3B Online
Master Gabster
Hy RogerB1941GMC, I believe the factory used 180 degree F thermostats. The truck probably came with a zero pressure cap when new, so any pressure would help stop the coolant boiling, you could contact the radiator company and ask if they have a suggestion. Years ago the factory started putting 190 degree thermostats in the engines, this made me nervous as the temperature was now ten degrees closer to the boiling point, but it doesn't seem to have created the problems I was fearing. Hope that helps.

Re: Proper Engine Running Temperature
RogerB1941GMC #1374819 Tue Aug 25 2020 08:19 PM
Joined: Feb 2004
Posts: 21,054
H
Boltergeist
If electric fans are so wonderful, why don't they use electric motors to turn airplane propellers? Is there some reason you don't want to run an engine-driven fan?
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Proper Engine Running Temperature
RogerB1941GMC #1374820 Tue Aug 25 2020 08:22 PM
Joined: Aug 2020
Posts: 59
A
Wrench Fetcher
The temp is controlled by the thermostat. Pull it out and see what temp it’s rated at to open. Anywhere from 180-200 is normal. Newer cars run warmer for emissions reasons.
The radiator cap determines system pressure. It also should have a value printed on it. It may be in psi, kpa, or even bar. Typical systems run 15psi / 100 kpa / 1 bar

Does it go up to 200 when your idling at a stop light?
Is this with or without the ac on?
With or without the electric fan running?
How many core aluminum radiator?


Pat
1940’s tech was great in the 40’s
Re: Proper Engine Running Temperature
RogerB1941GMC #1374822 Tue Aug 25 2020 08:29 PM
Joined: Dec 2008
Posts: 1,485
P
Shop Shark
If you use a pressure radiator cap it will tell you very quickly where every weak seam, loose clamp, worn hose etc. in your heater system is.
The damage from high water jacket temperature is that the engine will ping under hard load because the water nearest the exhaust valves and spark plugs in the head will boil, and allow that area to become hot enough to detonate. A pressure cap increases the boiling point and reduces the danger proportionate to how much pressure.

Re: Proper Engine Running Temperature
RogerB1941GMC #1374830 Tue Aug 25 2020 09:04 PM
Joined: Feb 2000
Posts: 4,178
J
Shop Shark
First off, 200 would be OK if it was mine as long as it stayed there or went lower. My replacement aluminum radiator came with a 19 lb cap, I switched to a 14 lb, the 250 can handle that and the new heater core can handle it. Your heater core will be the determining factor on pressure.

Lack of air flow is why it's heating up at slower speeds, you need a bigger fan, more powerful fan, or a mechanical fan made for A/C cars or trucks. It takes a lot of air to cool the condenser and radiator. All A/C cars had different pulleys and fans to move the air and coolant faster.

Re: Proper Engine Running Temperature
Hotrod Lincoln #1374848 Tue Aug 25 2020 11:28 PM
Joined: Jul 2000
Posts: 1,041
G
Shop Clutterist
Originally Posted by Hotrod Lincoln
If electric fans are so wonderful, why don't they use electric motors to turn airplane propellers?
Jerry

They do now!
https://www.harbourair.com/harbour-...rlds-first-commercial-electric-airplane/


Gord
----
1954 1/2 ton 235 4 speed
Re: Proper Engine Running Temperature
RogerB1941GMC #1374869 Wed Aug 26 2020 02:28 AM
Joined: Jun 2011
Posts: 3,632
E
Shop Shark
They do, but little range compared to IC engine.

Ed


'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
Re: Proper Engine Running Temperature
RogerB1941GMC #1374880 Wed Aug 26 2020 03:43 AM
Joined: Jul 2000
Posts: 1,041
G
Shop Clutterist
Just wanted to let Hotrod know that his crack to show his dislike for electric fans is out a date. I'm sure he can come up with something new.

For me, proper engine running temp is just past the E in TEMP.


Gord
----
1954 1/2 ton 235 4 speed
Re: Proper Engine Running Temperature
RogerB1941GMC #1374890 Wed Aug 26 2020 09:18 AM
Joined: Apr 2016
Posts: 101
A
ASU Offline
Shop Shark
look at where the temperature bulb is located. My 292 goes into the head right beside an exhaust port. It runs 210 all day, goes up to 225 on long hills. But the coolant going through the thermostat never goes above 185. Find a cheap Infrared temp gun to check it. some thermostat housings have holes tapped to put the temp bulb in.

Jon

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